Field of the Invention
The present invention relates to a touch sensor substrate provided with an electrode, a touch panel, a display device, and a method of producing a touch sensor substrate.
Discussion of the Background
In recent years, touch sensors are applied to operation units of various electronic devices, including mobile phones, mobile information terminals, ATMs, and car navigation systems. Such a touch sensor is bonded onto a display surface of an image display panel, such as a liquid crystal display device, as an input device for detecting a contact position of a fingertip or a pen point. Touch sensors are categorized into various types, such as resistive film type, capacitive type, optical type, and ultrasonic type, based on the structure and detection method of the touch sensors and are used with electronic devices depending on the applications. Among these types, from the perspective of having good durability, transmittance, sensitivity, stability, and position resolution, capacitive touch sensors, in which the electrodes do not contact with each other, are in mainstream use.
Capacitive touch sensors are categorized into a surface type and projection type. Both types use techniques of capacitive coupling. Capacitive coupling is caused by approach of an object having electrostatic conductivity, such as a finger, to the surface of such a touch sensor. The capacitive coupling between the electrode and the fingertip is captured by the touch sensor, for detection of the position (e.g., refer to PTL 1).
The surface type touch sensor includes a transparent conductive film planarly extending over a transparent substrate as a position detection electrode, and electrodes which are positioned at the four corners of the conductive film and connected to a driving circuit.
The projection type touch sensor includes a plurality of sensor-use conductive films extending in an X direction, which can be any direction, and a plurality of first conductive films extending in a Y direction, which is perpendicular to the X direction, as electrodes to be used for position detection. Such a position detection electrode is, for example, a mesh in plan view and exerts higher position detection accuracy as the arrangement pitch of the sensor-use conductive films and the first conductive films becomes smaller.
On the other hand, touch sensors described above are often installed on display surfaces of image display panels, and thus light transmission is required for either type of touch sensors. From the perspective of light transmission, the material for forming the position detection electrode is preferably a transparent conductive material having high transparency, such as ITO and ZnO, for example. However, with the upsizing of such touch sensors, an electrode formed from a transparent conductive material will have a greater length, and as a result, the electrode will have a higher resistance and the sensitivity for position detection will be lower. In recent years, it has been proposed to use metal having high conductivity which is capable of blocking light, as a material for forming the position detection electrode, with a thin wire shape to increase aperture ratio of the touch sensor.
A connection terminal that is an end of the electrode is bonded to a connection terminal portion of a flexible substrate to which a driving semiconductor device is mounted via an ACF (anisotropic conductive film). In this case, if the material for forming the electrode is a transparent conductive material, such as ITO, the connection terminal connected to the electrode is usually made of or covered with metal to decrease the contact resistance. In this regard, when the electrode is designed to be made of metal, the electrode and the connection terminal can be formed concurrently.
When electrodes are made of light-shielding metal and the plurality of electrodes are in a mesh shape in plan view, for example, the electrodes need to have a wire width which is so small, e.g. 10 μm or less, that they are not visually recognized. In addition, to minimize visibility of the thin wire electrodes, the reflective luster characteristic of metals has to be suppressed (e.g., refer to PTLs 2 to 4).
PTL 1: JP-B-4610416
PTL 2: JP 2014-016944
PTL 3: JP 2014-019947
PTL 4: JP 2013-129183